I. Field of the Invention
The present invention relates generally to reclaiming plastic during recycling operations. More particularly, the present invention relates to a method and apparatus for reclaiming component plastics from a mixture of plastics wherein differentials in specific gravity serves as the segregation mechanism.
II. Discussion of the Prior Art
Through time, plastics have enjoyed increasing popularity in forming articles of manufacture. This popularity, however, has given rise to a mounting environmental concern with regard to disposing the plastic articles after use. The resilient nature of plastic presents complications in that most plastics do not readily degrade in traditional waste disposal facilities, such as landfills, thereby creating the potential for future environmental hazards. The disenchantment with traditional waste disposal facilities has therefore prompted a host of activity in the area of plastic recycling and reclamation with the goal of providing reclaimed plastic for subsequent re-use so as to increase the effective lifespan of the plastics while decreasing the overall influx of plastics into traditional waste disposal sites.
U.S. Pat. No. 5,397,066 to Leitman et al. discloses one such attempt at reclaiming plastic for subsequent use. The process begins with a step of providing a mixture of two different plastics in the form of particles, inducing electrostatic charges on the particles of said mixture, and then introducing the mixture in the form of charged particles into a vertical fluidized bed column having an upwardly flowing gaseous stream therein. A fluidized bed column is provided designed so that a relatively low density fraction of the mixture consisting of a first plastic exits the upper end of the column, and a relatively high density fraction of the mixture consisting of a second plastic exists the lower end of the column. Another step involves charging the column with a polarity opposite that of the charge of the second plastic for attracting to the column the particles of the second plastic which are of relatively high density.
U.S. Pat. No. 5,358,119 to Stah et al. discloses yet another technique for plastic reclamation. The Stahl process utilizes density separation, a special surface treatment, and electrostatic separation to split up plastic mixtures into individual components. The plastics in the mixture are first ground into small plastic particles. The particles are then separated based upon their density. This is accomplished by placing the materials in a separation liquid which is selected so that the density of the liquid is between the greatest density and smallest density of the individual plastics. Once this separation is complete, each group of plastics separated in the density separation step are dried, injected into a fluidized bed and fed into an electrostatic freefall separator.
U.S. Pat. No. 5,227,758 to Brooks et al. sets forth a method for separating plastic coatings from paper labels or the like. The initial step involves introducing the plastic coated waste into a size reduction unit and reducing the plastic coated waste to particles having a maximum dimension range between about 1 inch and about 4 inches. Next, the plastic coated waste is mechanically hammered and rubbed in an effort to separate a portion of the paper from the plastic. The plastic is then floated in a slurry and agitated in an effort to separate still more of the paper from the plastic. The resulting plastic particles are further reduced in size to about 1/2 inch and then dried.
U.S. Pat. No. 5,115,987 to Mithal illustrates a technique for the separation of plastic beverage bottle components. The first step involves cutting the plastic bottle into two halves and then collecting the bisected bottle halves onto a moving take away conveyor. The bisected bottle halves are then subjected to a thermal treatment to soften the adhesives joining the beverage bottle components. The thermally softened bottle components are then set into a scrambler having an agitating means whereby the bottle components are mutually isolated and disjoined from each other. The disjoined components are then placed into a floatation tank whereupon the labels and high density polyethylene portions float while the polyethylene terephthalate components sink. The floating and sunken components are collected separately. Mechanical screening is then instituted to separate the plastic components from aluminum or other potential contaminants. The high density plastic components are subjected to air classification to separate the labels from the plastic.
U.S. Pat. No. 5,183,212 to Boo et al. discloses a method for separating a multi-layer plastic article into components. The method described in the patent in its most basic form is very simple, involving the steps of dividing the multi-layer plastic into small particles, agitating the particles and then separating one type of particles from the other type of plastic particles. This separation is achieved by flotation or through use of a centrifuge.
U.S. Pat. No. 5,104,047 to Simmons sets forth a waste treatment system which includes a waste receiving means, and a separating means for separating higher density material from lower density material. Each material can be subjected to a hammermill to produce an output of liquid slurry. The hammermill deposits the slurry in an elevator which dumps the slurry into a centrifuge to provide final separation of waste material from the slurry.
U.S. Pat. No. 4,830,188 to Hannigan et al. demonstrates yet another system for recycling plastic bottles. The first step in this process is to grind the bottles into mixed plastic flakes. The plastic flakes are then subjected to a wash liquid including a surfactant. The flakes are then placed in a liquid separator. High density flakes will sink to the bottom of the flotation liquid while the lower density flakes will tend to the float to the top. The role of the surfactant is to substantially reduce the surface tension of the liquid to assist in this separation based upon density.
U.S. Pat. No. 4,162,880 to Cobbs, Jr. et al. discloses a plastic scrap recovery apparatus which includes a hopper for receiving articles containing plastic material to be recovered, a cutter for breaking articles into chips, separating the chips into discrete component plastic materials, separating non-plastic components from the chips, conveying the chips and non-plastic components from the separator, melting a selected one of the discrete plastic component materials and pelletizing the discrete plastic component materials.
U.S. Pat. No. 4,809,854 to Tomaszek illustrates a system for reclaiming reusable resin materials from scrap articles. This system requires that scrap articles comprise at least one component formed of a first resin having a low density and a second component formed of a second resin having a higher density. The system described in Tomaszek includes a first flotation apparatus and a second floatation apparatus. The scrap particles are granulated and floatation separated in two successive stages.
U.S. Pat. No. 4,073,661 to Buzga et al. sets forth still another process for cleaning and preparing recycled plastics. First, foreign objects are removed from the plastic. The plastic is then fed into a washing solution having a greater specific weight than the plastic material. The washing solution and the plastic material therein are then subjected to a turbulent area and then advanced into a turbulent-free zone containing washing solution. The plastic is next removed from the turbulent free zone and dried.
The foregoing references address various problems associated with reclaiming plastics. However, notwithstanding this flurry of activity, the aforementioned references nonetheless suffer from a host of significant disadvantages. A need therefore exists for an improved method and apparatus for reclaiming component plastics.